I agree with Poofah, I upgraded my Whelp since it's farmed to extinction on both my servers, and it's a powerhouse.
The Flayer isn't a bad choice either, mine's currently level 20, it's not a utility pet like the Wolvar or some other Humanoid pets, but it's takes dragons apart and is good for the tamer dailies.
I would skip the Minfernal for now and wait for a class specific stone. While not an exploder, the Oily Slimeling
seems fairly easy to farm a rare of, and can really burn through pets.